1. Field of the Invention
The present invention relates to a plasma processing method.
2. Description of the Related Art
When a workpiece is to be processed with a plasma, e.g., when a thin film formed on a semiconductor substrate is to be plasma-etched, an apparatus having a vacuum chamber in which parallel plate electrodes are housed is used. The workpiece is placed on one electrode, and a plasma generation gas is introduced into the chamber. A high-frequency (RF) power is applied across the electrodes to generate a plasma from the gas, and the workpiece is etched by the generated plasma.
Recently, a low-pressure etching method is attempted wherein an etching is performed under a condition that a pressure inside the vacuum chamber is set at a relatively low level to control chemical etching contributing to anisotropic etching and to improve etching anisotropy. At such a low pressure condition, however, the density of the plasma generation gas is low, and the plasma tends not to be generated even if the RF power is applied across the parallel plate electrodes. Even if a plasma is generated, it takes a relatively long period of time to stabilize the generated plasma. That is, it takes a long matching time. In addition, reproducibility of plasma generation is degraded. This tendency becomes typical when the RF power is lowered and/or an interelectrode distance or gap is made smaller.
Thus, strong demand exists for stably and quickly generating a plasma at a low gas pressure even if an RF power is low and an interelectrode distance is small.